The present invention relates to a planographic printing plate precursor (hereinafter referred to also as a printing precursor) comprising an image forming layer containing heat-fusible particles and a method of manufacturing a planographic printing plate employing the precursor.
Recently, as computers spread, a computer to plate (CTP) process, in which a printing plate is prepared by imagewise exposing directly a planographic printing plate based on image information without using an original film, is spreading in planographic printing plate making. This process does not require a film-making process, resulting in cost decrease and in simplification of the process. Heretofore, a planographic printing plate precursor of either a silver salt diffusion type or a photopolymerization type has been mainly used as a printing precursor for CTP, but this type of the printing precursor requires an alkali development process for image formation. Synchronized with the spread of CTP processes and office automation in the printing field, a planographic printing plate precursor has been desired which does not require an alkali developing solution nor an alkali development process, in view of environmental concern.
There is disclosure in Japanese Patent O.P.I. Publication Nos. 9-131850 and 9-127683 of techniques regarding planographic printing plate precursors which do not require a development process. According to these techniques, a planographic printing plate is manufactured by imagewise exposing a planographic printing plate precursor having on a hydrophilic support a water developable image forming layer containing heat-fusible particles employing a laser, mounting the exposed precursor without development on a printing machine, and then developing it with dampening water or ink. The techniques provide a plate-making process, which does not need a special automatic developing machine nor a troublesome developing process to workers.
However, the techniques as described above are not still complete. When a printing plate prepared according to those techniques is subjected to treatment for increasing printing durability, non-image portions are difficult to clear at the initial stage of printing, and when printing is carried out employing a printing plate, which is prepared from a printing precursor accidentally rubbed by finger nails according to those techniques, stains are likely to occur at the rubbed portions during printing. It is very difficult to simultaneously solve the above-described problems. Further, the printing precursor has the problem that when subjected to treatment for increasing printing durability, its performances after storage are fluctuated.
The present invention has been made in view of the above. An object of the invention is to provide a planographic printing plate precursor which increases printing durability, prevents stains produced due to the finger nail rubbing, reduces loss of printed paper sheets at the initial printing stage, and minimizes fluctuation of its performances after storage. Another object of the invention is to provide a method of manufacturing a planographic printing plate employing the precursor.
The above object of the invention has been attained by the following constitutions:
1. A planographic printing plate precursor comprising a hydrophilic support and an image forming layer containing oleophilic heat-fusible particles, wherein the hydrophilic support has voids and the void content is 20 to 40 ml/m2.
2. The planographic printing plate precursor of item 1, wherein the hydrophilic support has pits on the surface on the image forming layer side, and the average radius (xcexcm) of curvature of ten pits is more than one-half of the average particle diameter (xcexcm) of the heat-fusible particles.
3. The planographic printing plate precursor of item 2, wherein the average depth (xcexcm) of ten pits is less than the average particle diameter (xcexcm) of the heat-fusible particles.
4. The planographic printing plate precursor of item 1, wherein the average particle diameter (xcexcm) of the heat-fusible particles is not more than 1.0 xcexcm.
5. The planographic printing plate precursor of item 1, wherein the heat-fusible particles contain a cross-linking agent.
6. The planographic printing plate precursor of item 5, wherein the cross-linking agent is an agent capable of combining with the hydrophilic support through a covalent bond or an ionic bond by heat application.
7. The planographic printing plate precursor of item 5, wherein the image forming layer other than the heat-fusible particles contains a cross-linking accelerator which promotes a cross-linking reaction of the cross-linking agent.
8. The planographic printing plate precursor of item 1, wherein the image forming layer other than the heat-fusible particles contains a cross-linking agent and the heat-fusible particles contain a cross-linking accelerator which promotes a cross-linking reaction of the cross-linking agent.
9. The planographic printing plate precursor of item 8, wherein the cross-linking agent is an agent capable of combining with the hydrophilic support through a covalent bond or an ionic bond by heat application.
10. The planographic printing plate precursor of item 1, wherein the heat-fusible particles have a melt viscosity of not more than 20 cps at 140xc2x0 C.
11. The planographic printing plate precursor of item 1, wherein the heat-fusible particles have a penetration of not more than 1.
12. The planographic printing plate precursor of item 1, wherein the hydrophilic support comprises a hydrophilic layer, and the hydrophilic layer contains a hydrophilic binder or film-forming hydrophilic particles.
13. The planographic printing plate precursor of item 12, wherein the hydrophilic support contains porous silica particles or colloidal silica particles.
14. The planographic printing plate precursor of item 12, wherein the hydrophilic support is a plastic film with the hydrophilic layer provided thereon.
15. The planographic printing plate precursor of item 1, wherein the heat-fusible particles comprise wax.
16. The planographic printing plate precursor of item 1, wherein the image forming layer contains oligosaccharides.
101. A planographic printing plate precursor comprising a hydrophilic support, and provided thereon, a heat-sensitive image forming layer containing oleophilic heat-fusible particles, wherein the hydrophilic support has pits on the surface and the average radius (xcexcm) of curvature of ten pits is greater than one-half of the average particle diameter (xcexcm) of the heat-fusible particles.
102. The planographic printing plate precursor of item 101, wherein the average depth (xcexcm) of ten pits is less than the average particle diameter (xcexcm) of the oleophilic heat-fusible particles. 103. The planographic printing plate precursor of item 101 or 102, wherein the average particle diameter (xcexcm) of the oleophilic heat-fusible particles is not more than 1.0 xcexcm.
104. A planographic printing plate precursor comprising a hydrophilic support, and provided thereon, an image forming layer containing oleophilic heat-fusible particles, wherein the hydrophilic support has voids and the void content is 20 to 40 ml/m2.
105. A planographic printing plate precursor comprising a hydrophilic support, and provided thereon, an image forming layer containing oleophilic heat-fusible particles, wherein the oleophilic heat-fusible particles contain a cross-linking agent.
106. The planographic printing plate precursor of item 105, wherein the cross-linking agent is an agent capable of combining with the hydrophilic support through a covalent bond or an ionic bond by heat application.
107. The planographic printing plate precursor of item 106, wherein the image forming layer contains a cross-linking accelerator which promotes a cross-linking reaction of the cross-linking agent.
108. A planographic printing plate precursor comprising a hydrophilic support, and provided thereon, an image forming layer containing oleophilic heat-fusible particles and a cross-linking agent, wherein the heat-fusible particles contains a cross-linking accelerator which promotes a cross-linking reaction of the cross-linking agent.
109. The planographic printing plate precursor of item 108, wherein the cross-linking agent is an agent capable of combining with the hydrophilic support through a covalent bond or an ionic bond by heat application.
110. The planographic printing plate precursor of any one of items 101 through 109, wherein the heat-fusible particles have a melt viscosity of not more than 20 cps at 140xc2x0 C. and a penetration of not more than 1.
111. A method of manufacturing a planographic printing plate, the method comprising the steps of:
(a) imagewise exposing the planographic printing plate precursor of any one of items 101 through 110 by means of a laser or imagewise heating the planographic printing plate precursor of any one of items 101 through 110 by means of a thermal head;
(b) mounting the exposed or heated precursor on a plate cylinder of a printing machine; and
(c) treating the mounted precursor with ink or a dampening water.